The present invention relates generally to speed responsive couplings and more particularly to friction shoe assemblies for use in centrifugally engaging friction clutches having limited torque transmitting capability. It has been found desirable to provide a lock-up clutch between the impeller and turbine of a fluid torque converter capable of connecting the impeller and turbine together under selected operating conditions and capable of releasing the impeller and turbine for relative rotation under other operating conditions. It has further been found desirable to provide a friction clutch which is capable of engagement at low rotational speeds, but capable of slipping at higher speed with increases in torque above the design level.
In the prior art it has been proposed to provide a centrifugally-actuated friction shoe in combination with a resiliently deflectable wedging ramp wherein the engaging force of the shoe with a drive surface, and therefore the torque capacity of the clutch, is determined by a combination of the mass of the shoes, the speed of rotation, the angle of the wedging ramp, the coefficients of friction, and the resiliency of the wedging ramp. In order to achieve rotational balance of a rotatable assembly, it is desirable to provide a plurality of friction shoe assemblies spaced circumferentially about the rotatable member. It has also been found that variations in the dimensional tolerance of ramp angles result in unequal distribution of torque capacity among the several shoes.
The present invention provides a friction shoe assembly for a speed responsive friction clutch that overcomes the disadvantages of previously known centrifugally-actuated couplings.